"On behalf of Americans everywhere, Michelle and I wish to extend our appreciation and prayers to His Holiness Pope Benedict XVI. Michelle and I warmly remember our meeting with the Holy Father in 2009, and I have appreciated our work together over these last four years. The church plays a critical role in the United States and the world, and I wish the best to those who will soon gather to choose His Holiness Pope Benedict XVI's successor."

British Prime Minister David Cameron said the pope "has worked tirelessly to strengthen Britain's relations with the Holy See."

"His visit to Britain in 2010 is remembered with great respect and affection," the British leader said. "He will be missed as a spiritual leader to millions."

Archbishop of Canterbury Justin Welby said he learned of the pope's decision "with a heavy heart but complete understanding."

He noted that in the pope's visit to Britain, he "showed us all something of what the vocation of the See of Rome can mean in practice — a witness to the universal scope of the gospel and a messenger of hope at a time when Christian faith is being called into question."

Irish prime minister Enda Kenny, who criticized the Vatican for its response to sex abuse scandals in Ireland, wished Pope Benedict well and said he had given "strong leadership" to the church.

"This is clearly a decision which the holy father has taken following careful consideration and deep prayer and reflection," he said.

"It reflects his profound sense of duty to the church, and also his deep appreciation of the unique pressures of spiritual leadership in the modern world."

The Archbishop of Dublin said the announcement was a surprise, even though it was clear the pope's health was fading.

"It's amazing that he has continued with a full schedule up until now," he said.. "Although it's very clear over the last month or so his health was declining."

"The attitude of the Vatican changed significantly under his pontificate," the archbishop said. "They took a much stronger line in relation to these issues," he said. "He was very interested in Ireland."

In Germany, the pope's home country, government spokesman Steffen Seibert said, "As a Christian and as a Catholic, one can't help but be moved and touched by this."

"The German government has the highest respect for the Holy Father, for what he has done, for his contributions over the course of his life to the Catholic Church," he added. "He has been at the head of the Catholic Church for nearly eight years. He has left a very personal signature as a thinker at the head of the Church, and also as a shepherd. Whatever the reasons for this decision, they must be respected."

German Chancellor Angela Merkel said she fully respected the pope's decision.

"If the pope himself, after thorough reflection, has come to the conclusion that he doesn't have the strength anymore to carry out his duties, then this has my utmost respect," Merkel said in a brief statement issued in Berlin. "He had to make a difficult decision."

French President Francois Hollande called the pope's decision to resign "eminently respectable," while Christine Boutin of the Christian Democratic Party expressed great surprise over the announcement.

"This is shocking, very shocking, unheard of for the Catholics and certainly for the entire world," she said.

"During his period [as pope] there were the best relations ever between the church and the chief rabbinate and we hope that this trend will continue," a spokesman quoted Metzger as saying. "I think he deserves a lot of credit for advancing inter-religious links the world over between Judaism, Christianity and Islam."

The World Jewish Congress said that the pontiff "elevated Catholic-Jewish relations onto an unprecedented level."

"No pope before him visited as many synagogues," WJC President Ronald Lauder said in a statement. "He met with local Jewish community representatives whenever he visited foreign nations. No pope before him made more strides to improve the relationship with the Jews - on so many levels."

House Speaker John Boehner, R-Ohio, an observant Catholic, praised Pope Benedict XVI in a statement and thanked him for his 2008 visit to the U.S. "The Holy Father's decision displays extraordinary humility and love for the Church, two things that have been hallmarks of his service," he said, "People of all nations have been blessed by the sacrifices he has made to sow the seeds of hope, justice, and compassion throughout the world in the name of Our Lord and Savior."

In Russia, Dimitriy Sizonenko, spokesman for the Russian Orthodox Church, said there is no reason to expect any drastic changes in the Vatican's policies.

"In its relations with Orthodox Churches, the Roman Catholic Church has always ensured continuity between popes," he said.

A spokesman for Philippines President Benigno Aquino said in a statement, "Not only the Catholic world, but all peoples and nations of goodwill are filled with great regret."

"We recall, in particular, with fond gratitude, the many prayers and comforting words Pope Benedict XVI has dedicated to Filipinos in times of calamity and challenge," the statement said.

The British newspaper The Guardian says Pope Benedict's abrupt resignation "heralds the end of a sad and storm-tossed seven-year papacy."

"The former Joseph Ratzinger came to the highest office in the Roman Catholic church with a reputation as a challenging, conservative intellectual," writes the Guardian's Rome correspondent. "But the messages that he sought to convey were all but drowned out, first by a string of controversies that were largely of his own making, and subsequently by the outcry — particularly in Europe — over sexual abuse of young people by Catholic clerics.".

"On the one hand, he was intellectually remorseless. Not for nothing had he attracted the nickname of 'God's Rotweiler.' Yet, like many scholars, Benedict was personally timid — wholly lacking in that desk-thumping vigor needed to foist reforms on clerics whose resistance to change is the stuff of legend."

In a particularly sharp reaction, Terry Sanderson, longtime president of Britain's 147-year-old National Secular Society, said that Joseph Ratzinger, who became Pope Benedict XVI, "played a major role in reducing the Catholic Church's popularity and its authority," and said that under his rule, "the Vatican has become despised and resented throughout the world."

"Joseph Ratzinger will now disappear from the scene," Sanderson wrote in his blog on the society's website. "Many will sigh with relief at his departure. But we shouldn't celebrate too soon. He has put in place a college of Cardinals that are as reactionary as he is – or even more so. Whoever they elect as the next Pope, there is unlikely to be much improvement."

Hans Kueng, a theologian who was an early colleague and friend of Ratzinger but later fell afoul of the Vatican for challenging church doctrine and became a vocal critic, told news agency DPA that he respected Benedict's decision — "but it has to be hoped that Ratzinger will not exert influence on the election of his successor."

He asserted that, given that Benedict has named many conservative cardinals, it would be hard to find someone "who could lead the church out of its many-layered crisis."